An optical fibre probe for use with a spectrophotometer, for remote analysis of samples, includes a probe assembly having an outer tubular body member, a sleeve member, and a further tubular inner body member within that. Input and output optical fibres pass into the assembly from one end, and the fibres are terminated in ferrules secured within a ferrule plate which is mounted by means of grub screws at the end of the inner body member. Radiation emerging from the end face of the input optical fibre is reflected back within the probe to be focused on the end of the other fibre, after total internal reflection in the case of an ATR probe or after passing through a transparent sample in the case of a transmission probe. Lateral positioning of the ferrule plate and thus the ends of the optical fibres, across the optical axis, is achieved by differential tightening of the grub screws. Focusing is achieved by sliding the inner body member longitudinally in the sleeve member, and also rotating the inner body member if necessary. The inner body member and the sleeve member are then locked together by fully tightening the grub screws.